Intermediate space transit planetarium



W. E. FRANK INTERMEDIATE SPACE TRANSIT PLANETARIUM June 21, 1966 7 Sheets-Sheet 1 Filed March 51, 1964 Ill-HIE nummmnnnu I INVENTOR WALLACE E. FRANK June 21, 1966 w. E. FRANK 3,256,619

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INVENTORI WALLACE E. FRANK June 21, 1966 w. E. FRANK 3,256,619

INTERMEDIATE SPACE TRANSIT PLANETARIUM Filed March 51, 1964 '7 Sheets-Sheet 5 INVENTORI WALLACE E. FRANK BY WMYSL June 21, 1966 w. E. FRANK INTERMEDIATE SPACE TRANSIT PLANETARIUM 7 Sheets-Sheet 6 Filed March 51, 1964 INVENTORI WALLACE E. FRANK Hols.

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INTERMEDIATE SPACE TRANSIT PLANETARIUM Filed March 51, 1964 '7 Sheets-Sheet 7 F IG. 9. HA7.

com cwb+ 8/00 @016 @036 no 6 up .9105 u Z 3/ y $5 .5706 L FIGlQ INVENTOFL WALLACE E. FRANK United States Patent "ice 3,256,619 INTERMEDIATE SPACE TRANSIT PLANETARIUM Wallace E. Frank, Westtown, Pa., assignor to Spitz Laboratories 111C. Yorklyn, DeL, a corporation of Dela- Ware Filed Mar. 31, 1964, Ser. No. 356,093

24 Claims. (CI. 3545) Planetarium instruments of the prior art have typically been devices which are capable of simulating the rotation of the star field about the pole star. Such instruments have also been capable of adjustment about a horizontal axis to adjust the elevation of the poles relative to the horizon in order to simulate observational points at different latitudes on the earth. The position of such an instrument in the planetarium auditorium has determined the selection of points to represent the location of cardinal points of the compass, and these remain the same unless the projected pole passes the zenith in which event there is a reverasal in the cardinal point.

As a result of this arrangement of the instrument,

planetariums in the past have been so constructed that the seating in the auditorium is in a peripheral ring facing inwardly. In this arrangement, inevitably some of the people in the room must look at the portion of the dome directly above them and behind them.

The planetarium instrument of the present invention is far more flexible than instruments of the prior art. It is capable of reorientation about a third vertical axis so that for any latitude any desired portion of the visible star field may be projected upon any desired meridian of the planetarium dome. Thus, it is possible to arrange the seating in the planetarium auditorium so that all seats face one portion of the dome and to reposition the instrument to project the area of the star field of greatest interest in this area. In this way the viewers may be submitted to a minimum of discomfort and a maximum of clear visibility. The same feature enables simulation of a change in the heading of an imaginary ship or vehicle in which the audience is supposed to be riding, including such vehicles as astronauts capsules and the like. Relative bearings may be maintained by supplying auxiliary projectors which indicate the heading or the changing positions of the cardinal points as the instrument is rotated about its vertical axis.

The flexibility of the instrument also results in greater flexibility of the auditorium which, because of the facing of the seats in one direction, is more conveniently usable for other purposes served by a conventional auditorium and to this end the instrument may be mounted on an elevator to lower it out of useful position.

The instrument of the present invention is provided with three axes of rotation, two of which, in preferred arrangements, are normal to the third. One of these axes, the number three axis, is preferably vertically oriented and serves to change the heading or meridian position of the projected star field with respect to the dome as previously described. The number two axis is a horizontal axis, preferably normal to the first and gimbal mounted on a yoke supported to rotate about the first axis. This 3,255,619 Patented June 21, 1966 second axis permits selection of elevation in a manner similar to that of the prior art. The number three axis is preferably normal to the second and provides the polar axis about which the star field rotates.

In addition to providing considerable flexibility with respect to the meridian, the instrument of the present invention provides a flexibility not heretofore possible. The celestial sphere can assume almost any position desired and diurnal rotation may be simulated about almost any polar axis through the star field. In fact, movements not familiar to earth bound creatures may be simulated, for example, to simulate an astronauts view while in some selected orbit. The use of the three axes permits simulation of many effects not heretofore possible with planetariums but its capability may be understood by consideration of various possible positions for the earth's axis and rotation of the star field about any of these positions. It will be observed that in order to simulate rotation of the star field about an axis other than the polar axis of the instrument, movement about all three axes will'have to occur simultaneously. The present invention permits use of a computer which is pre-programmed or capable of being programmed to provide the necessary simultaneous drive of the instrument about its three axes to cause effective rotation of the star field about an axis other than the instruments polar axis, or to simulate other desired movements. The instrument is capable of simulating a point of view whose position changes, as an astronauts would within the range between the surface of the earth and the moon and somewhat beyond. This is the first planetarium able to effectively simulate positions over such a range even from a rapidly moving vantage point.

The computer employed is preferably an analog computer and depends upon rotational position sensing means, as well as rotational drive means of each axis. In accordance with the present invention, the relatively rotatable structure at each of the three axes is provided with its own drive motor and with its own position sensing means, between which is a computer which may be programmed to require that the instrument assume in sequence predetermined positions programmed into the analog computer to cause the motions to combine into simulation of rotation of the star field about any predetermined pole, or some other effective motion.

The present invention also relates to a planet position analog projection apparatus similar to the types disclosed in my U.S. Patent No. 3,074,183, Jan. 22, 1963, entitled Projection Means for Planetariums. While the advantages and basic principle of the earth-sun-planet analogs described therein is retained, an improved construction is built into the analogs providing a higher degree of flexibility. In particular, two separate drive means are provided for each analog so that the relative positions of all three bodies simulated may be more quickly adjusted. As in said patent, the analogs are driven completely independently of the star field projectors. Furthermore in this improvement the effective position of the earth relative to the sun and the effective position of the other planets simulated with respect to the sun are each adjusted independently of the other and adjustment may be accomplished in moments. This adds considerably greater flexibility to the planetarium displays since, for example, it is no longer necessary to run clockwork at high speeds backward or forward to ready the instrument for projection of the positions desired at different times in history. Preferably, in fact, each analog drive motor is one component of a two-motor slave or selsyn system, the other of which is provided at a console so that positioning of the console motor to a predetermined angular position will cause similar positioning of the analog drive motor and positioning of the two console motors in circuit with the motors of a given analog enable on the spot 3 momentary adjustment at the console of any earth-sunplanet positions for a given analog.

Other improvements are also provided including improved projection arc lamps for the star field and improved lamp control circuits for controlling the relative brightness of the various planets and other celestial bodies.

For a better understanding of the present invention, reference is made to the following drawings, in which FIG. 1 represents in a schematic sectional, elevational view a planetarium according to the present invention, including the instrument, the domed auditorium and the console;

FIG. 2 is a plan view from above beneath the dome of the auditorium of FIG. 1 showing the location of the seats, the instrument, the console;

FIG. 3 is a schematic front elevational view of a planetarium instrument in accordance with the present invention much enlarged over the instrument represented in FIGS. 1 and 2 and with its polar axis made to coincide with the vertical axis for the sake of clarity in illustration;

FIG. 4 is a side elevational view of the planetarium instrument of FIG. 3 showing the polar axis position of FIG. 3 in dashed lines and showing in full lines the instrument rotated about its horizontal axis to an operable position;

FIG. 5 is a sectional view taken on line 5-5 in FIG. 3;

FIG. 6 is a much enlarged view partially in section along line 6-6 in FIG. 4 showing that portion of the instrument support frame associated with the vertical axls;

FIG. 7 is another enlarged sectional view taken on line 7-7 in FIG. 4 on substantially the scale of FIG. 6 showing among other things the frame and support structure of the planetarium instrument associated with its horizontal and its polar axes;

FIG. 8 is a diagrammatic representation of the relationship between the star field and the axes of the planetarium instrument;

FIG. 9 is a highly schematic circuit diagram representing one form of analog computer specifically useful in connection with the drive of the instrument of the present invention;

FIG. 10 is a much enlarged sectional view taken on line 10-10 in FIG. 3 of one type of arc lamp source for the star field projector;

FIG. 11 is a similar sectional view of the same source in different position;

FIG. 12 is an elevational view of the housing for the source when inverted;

FIG. 13 shows a modified star field arc lamp source;

FIG. 14 is a sectional view taken on line 14-14 of FIG. 7 showing the structure of a planet-earth-sun analog and its drives;

FIG. 15 is a sectional view taken along line 15-15 of FIG. 14;

FIG. 16 is a sectional view taken along line 16-16 of FIG. 15 showing the gear train maintaining the orbit inclination cam of the planet in correct orientation to the sun as it is revolved;

FIG. 17 is a still further enlarged sectional view, taken along line 17-17 in FIG. 3, showing the mirror structure associated with the analog of FIG. 14;

FIG. 18 is a schematic showing of the optical system associated with each planet analog; and

FIG. 19 is a circuit diagram of light brightness control circuit specifically useful in connection with control of the brightness of stars and planets in a preferred embodiment of the present invention.

Referring first to FIGS. 3 and 4, one embodiment of the planetarium instrument of the present invention is represented somewhat schematically. As seen in these figures the planetarium instrument has a base 10 which is supported upon the floor of the planetarium auditorium by means of leveling legs 11 which may be threaded or otherwise conventionally adjustable to permit leveling of the base. The base is a truncated four-sided pyramid as shown having a frame of angle irons or similar structural pieces welded or otherwise fastened together and housed in a suitable sheet metal cover. Rotatably supported relative to the base 10 is Y-shaped yoke generally designated 12. The downwardly projecting stem 13 of the yoke is rotatably supported with respect to the base structure to provide a vertical (number 3) axis of rotation for the yoke 12 relative to the fixed base. The spaced upper ends of the yoke provide a gimbal mount atop cage columns 14 within housings 15 for shaft 16. The cage construction here and elsewhere provides minimum optical obstruction. Shaft 16 provides the horizotnal (number 2) axis of rotation. It will be observed that shaft 16 and the horizontal axis it provides is normal to the vertical (number 3) axis provided by yoke stem 13.

The projector support frame 17, in turn, is rotatably supported on shaft 16 to provide an axis of rotation along its long axis normal to the horizontal axis, and to provide a polar (number 1) axis. The projector support frame 17 consists of a pair of columns each including cage structures 18 extending in opposite directions from shaft 16 and supporting at'its opposite extremities star field projection hemispheres 19a and 19b. Adjacent the shaft 16 are planet analog mounting decks 20 on which planet analogs 21, to be later described in detail, and related structure may be supported. The decks 20 may also support projectors for simulating other heavenly bodies as well as for special effects. Still other projectors may be supported on the horizontal deck 24 which is rotatable about the same vertical (number 3) axis about which yoke 12 rotates.

As will be appreciated by persons skilled in the art, rotation of the yoke 12 relative to the base 10 about the vertical (number 3) axis effectively changes the azimuth position of the instrument and the star field which it produces. In this way any ordinate point of the compass, such as North, or any other direction may be simulated at any desired meridian along the planetarium dome. If desired, suitable projection means for projecting points of the compass may be provided to move with the yoke 12 to identify the points of the com-pass relative to the star field projection on the dome. Rotation of the instrument projection system on support frame 17 about the horizontal axis on shaft 16 effectively produces simulation of the sky seen at any desired latitude on earth or corresponding position above the earth. In this connection, it will be appreciated that the hemispheric projectors 19a and 19b together present a complete celestial sphere which, however, is cut off at the horizon. Except in a vertical orientation of the polar axis, which is not permitted in a practical system as will be discussed hereafter, part of the projected star field is contributed by each hemisphere and correction is made for the separation between the hemispheres so that the star positions projected from each fall into correct relative position on the lprojection dome.

Finally, the number 1 or polar axis in accordance with the present invention need not correspond to the present polar axis of the earth although :for the sake of simplicity it may be so aligned in a given instrument. No matter what polar axis is provided, however, this instrument offer-s a flexibility to enable simulation of any other possible polar axis because of its capability of compound movements about all three axes. The effective polar axis, of course, is that axis about which the star field appears to rotate. The practical feasibility of translating the polar axes is, of course, dependent upon providing suitable drive means and sensing means in combination according to a program provided a computer. This computer which is preferably an analog computer is capable of determining the correct instrument position according to a program and instructing power servos which correct deviations of the respective axes from the positions sensed to the positions programmed. The computer function will be discussed in greater detail hereafter.

It has been common in prior art devices to incline the actual polar axis at an angle of 23 /2 to the perpendicular to the elevation or latitude producing axis corresponding to the horizontal axis in the present system. The angle 23 /2 is the angle made by the ecliptic pole to the equitorial pole. In preferred embodiments of the present invention since the instrument is capable of simulating any desired polar axis, no inclination is provided in the instruments polar axis and compensation for this departure from a true earth system is built into the projection equipment of the planet analogs and other projectors, as will be discussed hereafter.

From the discussion above it will be clear that the planetarium instrument lends itself to sufficient flexibility to permit projection of any meridian of the visible star field along any meridian of the planetarium dome. This instrument makes possible that portion of my invention directed to a new arrangement for planetariums. In this arrangement the seating instead of being in a ring tfacing inwardly to the center of the auditorium is arranged in more conventional auditorium fashion with the seating facing all in one direction, the direction in which the meridian including the area of the celestial sphere of greatest interest is to be projected. In this arrangement the console may be incorporated int-o a lecture desk or located at the rear of the room. A preferred arrangement is shown in FIGS. 1 and 2 wherein the instrument 1 is located beneath a conventional dome 2 in an auditorium of modified form. The seating which preferably is composed of benches 3, which may or may not be upholstered, is arranged so that the audience all faces in the same general direction. The benches may be arranged on an arcuate pattern as shown in FIG. 2 or in straight parallel rows, and they may be arranged on a floor 4 which is stepped, as shown, or one which is inclined or fiat. In the front of the room beneath the area of the dome on which the area of greatest interest is to be projected, may be provided a lecture desk 5, blackboards, and other auditorium or classroom equipment. The instrument controls may be incorporated in the lecture desk 5 or located at the rear of room in a separate console 6. The planetarium instrument may be mounted on an elevator, if desired, in order to be capable of lowering beneath the floor or out of the view of the audience when the auditorium is used for purposes other than planetarium shows. This planetarium arrangement facilitates greater use of the space and at the same time affords the planetarium audience greater comfort since the audionce will not have to look behind them for any substantial period of time. Any problem occasioned by shift of the field of greatest interest can be minimized if the audience is told to visualize themselves on a ship which is changing its course.

INSTRUMENT DRIVE AND POSITIONING SYSTEM The instrument drive and positioning system includes structure Ipermitting the relative rotation of the parts, separate means for rotationally driving each of the relatively rotatable parts with respect to one another and sensing means for sensing the relative rotational positions of said parts. These means are, in turn, an integral part of and control a computer system.

The drive means and structure associated with the vertical (number 3) axis are shown in FIG. 6 Whereas the drive means and associated structure in connection with the horizontal (number 2) and polar (number 1) axes are shown in FIG. 7. The drive means in each instance are preferably servo motors and may be a two-phase alternating current type capable of operating over a large range of speeds in order to facilitate position selection. The sensing means preferably are resolver type elements or any other suitable devices. One possible analog computer link and control is shown in FIG. 9.

Referring first to FIG. 6, the base 10 is shown in cross section and the stem 13 of yoke 12 is shown in its vertical position rotatably supported by the base structure. Rotational support near the bottom of stem 13 is provided by a support deck, generally designated 30. Deck is fixed to transverse supporting elements 31 fixed to the base frame adjacent its bottom. A bearing 32 of any suitable type is provided on the support deck 30 to receive and support a reduced diameter portion 33 at the bottom of stem 13. The tubular stern exends upwardly from this bearing and just below its junction with arms 14 is rotatably supported by a larger diameter bearing 35 of any suitable type but preferably a ball bearing having its inner race fixed to an enlarged portion 37 of the stem 13 and is outer race fixed to a bearing support ring 38 fixed to the base through spaced columns 39 extending above deck 40 at the top of the base to which they are fixed.

Servo motor 43 drives the yoke 12 about its vertically oriented (number 3 axis) defined by stem 13 supported on the base by its bearings 32 and 35. Motor 43 is supported on deck 30 by suitable support bracket means 44. The motor 43 drives the stem 13 through a suitable gear chain terminating in spur gear 45 which meshes with a large gear 46 fixed to the stem at the shoulder at which shaft diameter is reduced to portion 33.

The same large gear 46 drives sensing means 49 through a gear 47 and other gearing 48, all supported by deck 30 through suitable support structure 50. The sensing means 49 may be a resolver type or a differential transformer type or any other suitable type of sensing means capable of producing a signal useful with the analog computer link.

Separate from the yoke is the deck 24- which is rotatably supported from the base through deck 40, columns 39, bearing support ring 38, and bearing to rotate about the same vertical axis as yoke 12. The outer race of bearing 55 is connected to deck 24 through suitable structure 56. Also connected to this structure and through it to the deck 24 is large ring gear 57 which is driven by motor 58 in order to produce rotation of deck 24. It

should be noted in passing only one full rotation of the deck is permitted and preferably stop means limits rotation beyond some selected point in either direction. Motor 58 is supported 011 deck 41) of the base and through a suitable chain of gears 59 drives spur gear 60 which meshes with and drives ring gear 57. Thus, it will be seen that support deck 24, which is provided to carry auxiliary projectors of various types, may be positioned completely independently of the position of the yoke 12 relative to the base. This again gives added flexibility to all auxiliary projectors which may be employed with the planetarium instrument and mounted on this deck 24,

Referring now to F-IG.- 7, the upper ends of the cage columns 14 which terminate the yoke structure 12 are shown in greater detail. Atop these columns the gimbal housings 15 serve to enclose at least partially the motors and sensing means for the horizontal (number 2) axis. Bearing support is provided by plates 69 which are fixed to the top of the respective columns 14 and which carry bearings 61 in which the shaft 16 is journaled. The drive means is provided by motor 63 which is mounted within the housing 15 shown in section atop columns 14. The shaft of motor 63 drives through a gear chain 64 supported on plate 60 to an output gear 65 which meshes with spur gear 66 fixed to and driving the horizontal shaft 16 about its axis. The drive, of course, is provided on only one side although gimbal mounting provides symmetrical bearing support from both sides of the yoke structure 12. A suitable sensing means 68 is provided at the end of the shaft coupled thereto through gearing so selected that the sensing means rotates at the same speed as the structure whose rotation it is sensing, all of which is supported relative to the plate 60.

The projector support frame 17 is, in turn, supported to rotate relative to shaft 16 about the polar (number 1) axis. This is accomplished by providing similar support means 72a and 72b opposite sides of the shaft which support substantially identical columnar structures. Support means 72a and 72b provide a mount for bearings 73a and 73b which rotatably support tubular stern elements 74a and 74b, respectively. These stems would be capable of independent rotation were it not for the common gear connection, to be described, which keeps them synchronized. Also supported on the shaft 16 are t-ubular housing members 75a and 75b (which may be a single tubular member) having rigid end plates 76a and 76b which support bearings 77a and 77b. These bearings support and permit rotational movement of support stems 47a and 74b at positions spaced from the bearings 73a and 73b. Outwardly from shaft 16 the support columns 18 broaden out from the tubular stems 74a and 74b, and this increase in diameter is accomplished through the medium of an annular flange 78a and 78b on which the cage columns 18 are based. Also supported from the flanges 78a and 78b are cylindrical skirts 79a and 7% which carry the planet analog supporting decks 20a and 20b so that these decks rotate with the columns. Skirts 80a and 80b cover and protect the drive mechanisms for the planet analogs and any other structure which it may be desirable to house within them.

Returning to the drive structure for the polar (number 1) axis, it will be observed that the motor 82, again preferably a servo motor, drives through a gear connection, a jack shaft 83, which bears two separate spur gears 84a and 84b which mesh, respectively, with gears 85a and 85b on the reduced diameter portions near the base of tubular stems 74a and 74b. Thus, the columns 18a and 18b are driven in synchronism so that the star field hemispheres 19a and 19b at their respective ends are kept in step.

Since the respective parts are synchronized properly, a sensing motor, or other sensing device, 87 may be suitably connected through igear 84b and other gearing 88 to sense the position relative to the polar axis of the columns 18a and 18b at all times. Both the motor 82 and the sensor element 87 are supported on the structure connected to the horizontal shaft 16 in this system. It will be appreciated here, as in connection with the other axes, that the motor housing may be connected to either one of the relatively rotatable parts and the shaft connected to the other as in any system of this part.

COMPUTER The provision of servo motor drives for each axis and sensing means to sense the angular position of each axis makes it possible to control the system described by computer. The computer may be programmed to drive the respective axes in predetermined sequences of motion to accomplish any desired sequence of positions of the celestial sphere relative to the viewer such as the changing view of the heavens experienced by an astronaut in selected patterns of orbit around the earth, around the moon or between the earth and the moon. For programs .of closely related repetitive patterns an analog device may be employed.

For example, the analog computer of FIG. 9 may be used to shift the effective axis of rotation of the star field. It will be seen that the servo motors 43, 63 and 82 are part of this system and that the sensing means 49, 68 and 87 are part of the system as well. Before proceeding with a description of the computer, an analysis of the function it performs will be made with reference to FIG. 8 which is a diagram of the celestial sphere in terms of location of the axes of the planetarium instrument and the effect sought to be achieved.

Referring to FIG. 8, the celestial sphere is represented as a globe. Planetarium instrument axes are represented in terms of their numbers, the numbers in the diagram being encircled. It will be appreciated that points representing stars or the like on the sphere or globe change position as rotation occurs about any one axis. Thus, if rotation occurs from the position shown about axis 3,

ulates the familiar star field rotation about the earths polar axis.

If vertical and horizontal axes 3 and 2 are fixed in position and rotation is maintained about polar axis 1, the star field will appear to rotate about a projection of axis 1 through the earths pole star. Rotation about the number 1 axis for a given position of the number 2 axis is the simplest type of situation and one analogous to the one commonly employed in the prior art, i.e., where the polar axis and the axis of rotation of the star field coincide.

The present invention permits solution of the more general problem of simulation of some point on the celestial sphere other than the pole star as the locus of the polar axis of rotation of the star field or celestial sphere.

If now we assume that the polar axis and the axis of rotation of the star field are to be different, it will be obvious that the point in the star field which appeared to be stationary during rotation about the polar axis must move in a circle represented by the dashed line about the new point and more particularly about an axis P through that stationary point on the celestial sphere and the center of the sphere. Effectively the number 1 axis must be revolved along the path of the dashed-line circle. Such motion necessitates a compoundmovement about the other two axes. At the same time rotation about axis 1 is required to simulate rotation of the stellar field. An oscillatory movement about axis 2 must be superimposed upon the rotational polar movement to effect that component of movement producing changes in latitude of axis 1, which may be visualized by projecting the position of axis 1 on the meridian. Similarly, an oscillatory movement about axis 3 is required to effect the component of movement producing changes of axis 1 from one meridian position to another which may be visualized by projecting the positions of axis 1 on the equator. Since the axis 3 is the only axis which remains effectively fixed in space, it may be taken as one reference vertex of a triangle drawn on the celestial sphere. Another reference point is the point at which axis P, which is selected as the point of rotation of the star field, penetrates the celestial sphere. Finally a constantly changing point on the locus of the dashed circle represents the instantaneous position of axis 1. The spherical triangle constantly changes size and shape as polar axis 1 moves about the dashed-line circle. However, at any instant of time the following is true:

b is the are between the zenith and pole P (arc from axis 3) (observer co-latitude); and c is the angle of axis 1 with respect to axis 3, determined by the position of axis 2 (first axis selected co-latitude). On the basis of these definitions, the following identities may be written:

cos c=cos a cos b+sin a sin b cos C sin B=sin b sin C/sin c sin A=sin a sin C/sin c become infinitely large. This condition clearly cannot be tolerated in the construction of a practical system.

1 sinc is a measure of coincidence of the axes which is found to recur in the analytical expressions for system performance. It is felt to be desirable to maintain M less than or equal to in order to allow the system to perform in a satisfactory fashion for the bulk of the problems. As a practical matter, this presents a forbidden angle of 6 from coincidence of the axes. It may be de=mon strated that the probability of a problem selected at random entering a forbidden zone of 6 half angle is of the order of one part in two hundred. In accordance with the present invention the 6 forbidden zone will be avoided by means of circuitry which will flatten the normally circular path of a star on the dome when the true path would force it into, or too close to, the forbidden region. This correction will take place over a range of displacement of axis 2 of from 6 to 12 from the pole so that the number 2 axis will be limited to an excursion of 184 from the horizontal.

The computer of the present invention must be capable of providing the required rate of rotational or oscillatory drive to each of the motors involved in order to simulate the conditions sought to be presented. The computer must take position information as set on the dials 90, 91 and 92 and, on the basis of the position sensed, cause the rotational position of each of the axes to change simultaneously such that the desired effect will be achieved, both with the apparent simulation of a selected pole P and subject to the flattening of the arc in the region of the approach of axis 2 to the forbidden zone surrounding axis 3.

Referring now to the block diagram of FIG. 9, it will be observed that there are a number of dials which are representative of the angular or are parameters diagrammed in FIG. 8 and described above. In particular, there are six dials 90, 91, 92, 93, 94 and 95, representative of the parameters a, b, C, B, A and c, respectively. The arcs a and b are selected by manually setting dials 90 and 91. For a given problem involving rotation about a simulated pole P, these dials and the shafts they position ordinarily remain fixed once set. The angle C is variable with the time of day by means of a drive motor 96 but the dial 92 is positioned before beginning operation to determine the angle for a starting time during the day. The angles A and B represented by a particular selected spherical triangle like that shown in FIG. 8 and are c are variable but their values are determined uniquely through the action of the computer and are indicated by the dials 93 and 94 representing angles B and A, respectively, while dial 95 indicates the are c. Dials 93, 94 and 95 are not means of manually positioning shafts like dials 90, 91 and 92 but are shaft position indicators, and the shafts whose positions they indicate are automatically deter-mined by the axis position sensing means. Changes dictated by the computer are imposed by means of drive motors 82, 63

M x (the absolute value of and 43.

The manual setting of dial 90 determines the shaft position, and hence the coupling factor influence upon the respective outputs of two resolvers 100 and 101 which, for example, may be in line and sharing a common shaft. Similarly, the shaft position determined a manual setting of dial 91 determines the outputs of resolvers 102 and i0 103. Finally, the shaft position determined by dial 92 and motor 96 determined the continuously variable outputs of resolvers 104 and 105.

.When a position change in axis 1 is required, the electrical output of resolver 1.06 drives servo motor 82'. Servo motor 82 thereupon changes the position of the selsyn 8'7 and indicator dial 93 as it corrects the position of the shaft of resolver 106. As a consequence sensing selsyn 87 seeks to change position to correspond to the position of position 87. The signal seeking to reposition the selsyn is amplified and used to drive motor 82 which does reposition the axis 1 of the instrument and the shaft of sensing selsyn 87 until it corresponds to the' position of selsyn 87'. In a similar fashion the position of the axis 3 shaft is changed as drive servo motor 43 responds to the output of resolver 107 and changes the position of selsyn 49 and indicator dial 94 as it corrects the position of resolver 107. Selsyn 49' in adjusting causes selsyn to seek to assume a similar position to the position of selsyn 49. The signal seeking to reposition the selsyn 49 is amplified and used to drive motor 43 which does reposition the axis 3 of the instrument and the shaft of sensing selsyn 49 until it corresponds to the position of selsyn 49'. Likewise, the position of the axis 2 shaft is changed as servo motor 63 responds to the output of resolver 108 and changes the position of selsyn 68 and indicator dial 95 as it corrects the position of the shaft of resolver 108. Selsyn 68 in adjusting causes selsyn 68 to seek to assume a similar position to the position of selsyn 68'. The signal seking to reposition the selsyn is amplified and used to drive motor 63 which does reposition the axis 2 of the instrument and the shaft of sensing selsyn 68 until it corresponds to the position of selsyn 63'. Since selsyns 82', 4-9 and 68 asume positions representative of their respective axis positions, the dials 93, 94 and 95 are automatically positioned to represent and read out positions of these axes.

The electrical outputs of the various resolvers are usually two in number, the output from one winding giving the sine of the angle of the shaft and the output from the other output winding giving the cosine of the angle of the shaft. If a simple reference signal is given, as in the case with resolvers and 103, simply the sine and cosine of the shaft angles will be produced in the respective output Winding. Thus, the outputs from resolver 100 are sin a and cos a, and the outputs of resolver 103 are sin b and cos b. However, where one of these simple electrical outputs is fed as an input signal into another resolver, the output is a product of that input and each of the respective sine and cosine of the angle represented by the shaft of the resolver. Thus, the outputs of resolver 104 are sin a and cos C and sin a sin C. In similar fashion,

the output of resolver 105 which takes the sin b output from resolver 103 is sin b cos C and sin b sin C. Since a pair of outputs are fed to each of the resolvers 101 and 102, sum and difference outputs are obtained as outputs of these resolvers. In the case of resolver 101, only the output cos b sin a sin b cos a cos C is used. In the case of resolver 102, both outputs cos a cos b sin a sin b cos C and cos a sin b sin a cos b cos C are used. By identities these sum and difference expressions can be rewritten as monomials specifically sin 0 cos B; cos C; and sin 0 cos A. Booster amplifiers may be used as shown where there is the possibility of los or distortion of the signal.

As seen in FIG. 9, resolver 106 is fed signals sin c cos B from resolver I01 and sin 0 sin B from resolver 105 and its output is used to drive motor 97 to reposition its shaft and the shaft of synchro 82'. The shaft output will be B which is the adjustment required of axis 1. Resolver 107 is fed signals sin 0 cos A from resolver 102 and sin 0 sin A from resolver 104. Its cosine output is used to drive motor 98 which rcpositions its shaft and axis 3 through synchro 63 to proper A position. The sin 0 output is fed to resolver 108 along with a cos 0 signal from resolver 102 and causes resolver 108 to drive 1 1 motor 99 to reposition the resolvers shaft and the shaft of synchro 43 to proper position.

Thus by proper selection of a, b and C through settings of dials 9t), 91 and 92, a correct output is obtained of the constantly varying B, A and 0 values needed to adjust instrument axes 1, 3 and 2, respectively. I

By additional analog procedures, should the dashed circle path of the polar axis 1 be required to enter the 6 forbidden zone, the path would be flattened in the region of approach to the forbidden zone, for example, by appropriate inhibition of the movement of axis 2.

LIGHT SOURCES The light source for the star field simulation of hemisphere 19a is shown generally as element in FIG. 3. This same element is shown in section in FIG. 10. As shown in FIG. 10 a preferred light source is an arc lamp 131 which has its electrodes out of alignment, i.e. at an angle of less than 180 within a transparent envelope of quartz or other suitable material. For the sake of clarity, electrical leads are omitted, but it will be appreciated that leads connecting the lamp to a suitable power source are connected to the external terminals of each electrode. The arrangement of the electrodes at an angle to one another instead as in line as is more conventional enables the lamp to provide more than a full hemisphere (i.e., 180 solid angle) of light without a significant shadow from the electrodes. In the structure shown in FIGS. 10 and 11, the lamp is mechanically supported at one end by block 132 on a deck 133 associated with a series of light baffies 134, 135 and 136 on the support frame side of the light in the form of generally parallel decks at different levels supported relative to one another by columns and staggered to provide a tortuous path against the escape of light toward support frame 17. The deck 136 also supports transverse baflies 137 and 138, which further inhibit light leakage, and is the support means for the lamp structure whereby it is connected by columns to the base 140 of star field projection hemisphere 19a. Base 140 is, in turn, connected by a series of support posts to a ring 141 fixed by screws or other suitable means to end plate 142 of column 18a. Enclosing the light source 131 and supported on a suitable cushioning member 145 against deck 136 by a clamping ring 146 is a flange 147a of a horizon simulating structure 147. This structure is in the shape of a bell jar having double walls sealed together at flange 147a between which walls are provided a predetermined amount of fluid 148, such as ethylene glycol with dyes or the like which are opaque to light, or sufliciently filtering to eliminate substantially all visible rays. This device is designed so that it provides as much illumination as a solid angle of 196 in its uppermost position shown in FIG. 10 and 164. solid angle of illumination in its lowermost position, shown in FIG. 12. Of course, in the lowermost position the bounds of the hemisphere occlude a large part of the solid angle, that part which is projected by the other hemisphere.

As the horizontal axis (number 2) of the planetarium instrument is adjusted, the instrument support column changes position so that the light source will assume positions other than the extreme positions shown in FIGS. 10 and 12. For example, the position shown in FIG. 11 is that represented by the position of the instrument in FIG. 4. As the instrument moves, the fluid shifts position, always maintaining its surface, and hence the simulated horizon line cutting off the projected star field, horizontal or parallel with a horizontal floor.

In accordance with my invention the light source of insulated from the terminals and which has an axis of rotation provided by shaft 153a of motor 158. Motor 158 is mounted on part of the instrument support structure 17, the support 159, so that its shaft lies along the polar axis. Also mechanically constituting part of the instrument support structure but electrically insulated from one another and from the structure are slip rings 160 and 161, respectively, connected to terminals 154 and by brushes 162 and 163 which maintain sliding contact with slip rings and 161 as the light source 150 rotates. A direct current power source 164 connected between the slip rings 160 and 161 will provide the power to maintain illumination of the lamp 150 once an arc has been produced between electrodes 151 and 152. Since these electrodes are aligned, they and their supporting structure will throw shadows so that a full solid angle of cannot be obtained. However, by rotating the whole structure, the position of the electrodes is constantly varied so that in the aggregate the shadow of the electrodes and the supporting structure is largely washed out since it occurs in any one place for such a small part of the total time. In this way a clear unobstructed light source may be obtained over a solid angle equal to or exceeding a hemisphere.

PLANET ANALOGS Turning now to a consideration of planet analogs 21, already identified in FIGS. 7, 3 and 4, a detailed representation of an individual planet analog is seen in FIGS. 14, 15 and 16. The reflecting mirror omitted from FIG. 14 is seen in FIG. 17 and a complete optical system for a planet analog is illustrated in FIG. 18. I

The theory of the operation of the planet analog systems will permit planet analogs to be mounted on either deck 20a or 20b (see FIGS. 3 and 4) and, regardless of the place of mounting, they are essentially the same in theory of operation. Since each is mounted off the polar axis, some means of correction for this location and the errors that would otherwise be produced must be provided. Moreover, the various idiosyncrasies of the individual planets must be built into the analog elements so that there are differences based upon size of orbit, inclination of the plane of orbit to the ecliptic plane and efifects introduced by the polar angle of declination. All of these factors are taken into consideration in each of the analogs which, although they are built essentially alike, must be capable of individual adjustment to simulate the idiosyncrasies of a particular planet.

As explained in my Patent 3,074,183 in considerable detail, it is possible to construct analogs which assume either that the sun revolves around the earth or around one of the planets to be simulated and that the planet or the earth as the case may be, revolves around the sun. In the case of the inferior planets such as, for example, Venus and Mercury, the analog assumes that the sun is revolving around the earth and the inferior planet is revolving around the sun. In the case of superior planets, such as Mars, Jupiter and Saturn, for example, the assumption is that the sun revolves around the planet and that the earth revolves around the sun. As explained in considerable detail in that patent, by assuming that this is so, an assumption which is possible, it is possible to use the line of sight between the earth and the planet achieved by the analog as the direction in which the light simulating the planet must be projected. In the case of inferior planets, the line of sight is from the earth to the planet so that the direction is correct for projection of light. However, in the case of superior planets, the line is from the planet to the earth so that the direction for projection of light must be reversed.

The analog in accordance with the present invention is essentially the same as that employed in the previous patent. However, structurally, certain changes have been made which yield considerable advantages in greater flex- 18 ibility in the overall analog. In particular, separate drive motors have been provided for simulating the movement of the sun around the earth or the planet and for simulating the movement of the earth or the planet around the sun. The analog shown in FIGS. 14, and 16 simulates Mercury, an inferior planet, and in this instance, the earth is taken as the center of the analog system. The sun revolves around the earth driven by one motor and Mercury is caused to revolve around-the sun, wherever it is, by another motor. The use of separate motors enables the positions of the sun relative to the earth and, in this case, Mercury relative to the sun, to be independently accomplished, thereby saving the substantial amount of time which would be necessary in some instances to adjust from a position represented by a planet at one period of time to a position represented at a much different period of time. Referring to FIG. 14, it will be first observed that the analog and its drive unit are easily removable from the deck 20 so that a defective unit can be readily replaced as required. The base 180 of the analog unit is provided with a stepped shoulder to fit sungly into an opening in the mounting deck 20. Circumeferential grooves 180a and 18% provide alternate means of securing the analog unit to the mounting deck 20. In the embodiment shown, brackets arranged around the periphery of the base 180 enter groove 180a and, in turn, are held in place against the base by screws. Drive means 181 and 182 are supported by suitable support brackets from the base 180. The shaft of motor 181 is coupled to a shaft through the base 180 to drive gear 183 which, in

turn, drives gear 184 and the turntable deck 185 to I which it is connected about a central spindle 186 fixed to the base 180. In this particular analog the suns position is taken as some point on the deck 185, and more specifically as the positon of shaft 187. Shaft 187 is coupled to a deck 188 which has a post 189 mounted on it whose axial position as it rotates around shaft 187 simulates the position of the planet Mercury with respect to the sun and its analog. Shaft 187 is driven by motor 182 through a series of gears 191, 192, 193, 194, 195, 195, 197, and 198. These gears are supported on shafts as follows: gear 191 on shaft 200 connected to the motor shaft through base 180; gears 192 and 193 on shaft 202 on opposite sides of base 180; gears 194 and 195 on shaft 203 through the base and center of rotation of deck 185; gears 196 and 197 on shaft 204 through the deck 185; and gear 198 on shaft 187 on the opposite side of deck 185 from the planet analog structure to be described. In practice, the relationship of the gears may be seen from the shaft locations pictured in FIG. 15. However, the gear chain can be better visualized from FIG. 14 which is somewhat distorted to present the gears spread out in line so that the gear chain may be more clearly understood.

Since the common axis of spindle 186 and shaft 203 in this instance represents the locus of the earth and the axis of post 189 represents the locus of Mercury, the common plane of the axes defines the azimuth of Mercury and a straight line may be drawn in that plane representing the line of sight from the Earth to Mercury. A light beam projected along this line will give the correct position of Mercury at that time. In accordance with the present invention, this straight line of sight is simulated by providing slide rod 210 which has a pivoted connection 211 to coupling member 212 on the central earth axis such that the pivot is normal to that axis. Member 212 is rotatable independently of the axial structure from which it is supported. The axial position of coupling member 212 is preserved by its axial cylindrical pin appendage 212a which is received within a tubular guide member 213 and its level maintained by set screw 213a which cooperates with a circumferential groove to maintain the axial level of member 212. Tubular guide member 213 relative to which. coupling member 212 is rotatable may be fixed to one end of shaft 203, for example, in which case it rotates with shaft 203 whereas 14 member 212 follows slide rod 210. The slide rod 210 also passes diametrically through ball 215 which is seated in a recess or socket on post 189 and magnetically or otherwise held in place so that it is free not only to rotate generally about the Mercury axis of post 189 but facilitates elevational changes as will be described.

The orbit of the planet simulated about the sun relative to the ecliptic plane must be considered in determining the elevational position of the planet. Since the earths orbit defines the ecliptic plane, a single cam compensator is normally all that is required. Since the plane of the orbit of Mercury around the sun lies 7 out of the ecliptic, a cam 220 provides proper positioning of deck 188 to simulate changes in elevation of Mercurys orbit.

out of the ecliptic plane. Thus, as the deck 188 rotates about axis 187, the position of ball 215 rises and falls depending upon what portion of cam 220 it is over, and this simulates the particular deviation from the ecliptic assumed by the planet in the various parts of its orbit. It will be apparent that, since the ecliptic plane may be taken as any plane parallel to deck such as the plane through pin 211, deviations in the position of Mercury imposed by cam 220 cause slide rod 210 to assumea proper line of sight simulation.

The position of cam 220 must not change as the sun appears to revolve about the earth since Mercurys orbital plane would otherwise appear to rotate about the sun rather than remaining fixed as it actually does for all planets. In order for the orbital plane to maintain its position fixed relative to the sun, the cam 220 must be driven one revolution for each revolution of the sun about the earth. A gear arrangement provided for this purpose produces rotation of the cam in the opposite direction from revolution about the earth in order to maintain the apparently fixed relationship. This is accomplished employing gear 222 fixed coaxially to the cam 220. As seen in FIG. 16, gear 222, in turn, is driven through a chain of gears 223, 224 and 225 back to the center shaft so that it rotates at the same rate as the deck 185 but in the opposite direction.

It will be apparent that the rotation of the planet about the sun is not altered by the cam 220 but the apparent elevation is changed in accordance with the rotation of the ball 215 with respect to cam 220 and pin 212a rotates relative to tubular member 213. As the azimuth changes, the rod changes direction as the ball 215 rotates relative to post 189. As the elevation changes, the rod 210 pivots about pin 211. Thus, the slide rod, despite the various limitations on the system, is always able to assume the correct azimuth and the correct elevation to assume within the analog a correct line of sight position between the earth and the planet Mercury.

Because the planet analogs are located off center of the polar axis of the instrument, a small error of parallax is introduced which is corrected in accordance with this invention by a relatively simple expedient not heretofore recognized or employed in other planetariums. The rod 210 is terminated in a post 227 which is fixed to the rod so that the axis of the post is generally parallel to the earth and Mercury axes when rod 210 is in the ecliptic plane. Post 227 provides a socket, similar to that in post 189, which receives a ball 228, similar to ball 215 and in a similar manner. In this case, 'slide rod 229 passes diametrically through the ball 228 and is pivot-ally connected by a pin 230 which, although it is offset from the axis of rotation of the bearing mounted spindle member 231, causes the rod 229 to pass through the axis. The amount of offset between the axes of rotation of the shaft 203 simulating earth position and spindle 231 is analogous to the amount of offset of the analog from the center line of polar axis of the instrument. The ratio of the offset of the axes to the analog planet position is proportional to the ratio of offset of the analog center from the planetarium instrument polar axis to the distance from instrument to dome of the planetarium. This simple proportional correction may save noticeable errors and is, therefore, worthwhile in light of the overall accuracy of the system. While in the instance illustrated the correction makes the circular orbit concentric with the sun, in other situations the same effect may be used to effectively shift the center of a circular orbit not concentric with the sun.

The position of a tube 233 axially aligned with and mechanically connected to rotate with the spindle 231 as seen in FIG. 14 determines the azimuth heading of the mirror 235. The push rod 234 in sliding engagement within tube 233 determines the elevational position of the mirror 235, as will be described, in accordance with the lever action of slide rod 229 upon the push rod. Movement reflecting elevational changes is applied at ball 228 and, since the fulcrum supplied by pin 239 is fixed, a smaller axial movement proportional to planet elevation is imposed on push rod 234. Dust cover 240 transparent for convenience in explaining the planetarium planet analogs, provides a bearing 241 for the spindle 231. For this reason some precision is required in the construction of the cover 240 and its connection to base 180.

Analogs for different planets vary primarily in the relative locations of the earth or planet axis, whichever revolves about the sun in the analog and on the selection of a cam which is specific to the particular orbit of each planet. It will be understoodthat the same analog can be used for both inferior and superior planets. The suns position relative to the earth or planet axis center of the analog may be arbitrarily fixed in either event so that only the earth or planet axis revolving about the sun axis need be varied from one analog to another since the analog system need only be maintained proportional within itself and not relative to other analogs. This means that the position of post 189 on the support deck 188 must be varied from analog to analog depending upon the planet simulated. It means too that the orbit inclining cam 220 must be appropriately selected. However, the invention provides a means whereby one or two spare analog systems and a supply of decks and earns for each planet displayed may economically be kept on hand so that defective analogs may be quickly replaced by removal of one analog system and substitution of another in its place on deck 201.

One problem arises with respect to the points of intersection of the orbit of a given planet with the ecliptic. This can be provided for by providing a registry mark on the base 185 and a mark on each of the cams so that the cam will assume the proper orbit orientation when the marks are in registry. With the point of intersection of the orbit with the ecliptic established, it is then only necessary to adjust the elevation of the simulated planet, and this can be done at the mirror.

Referring now to FIG. 18, a schematic representation of the relationships of the projector light source, light path determining mirrors and the analog used in a planet simuation system is illustrated. The projector light source 237 is mounted on the same deck as the analog 21 in prefered embodiments. The light beam produced by the projector 237 is reflected from surface silvered mirrors 238 and 239, both of which are supported by the support deck 140 (FIG. 10) for the hemispheric star field projectors, in this case 1912, such that light is reflected back to mirror 235. The position of shaft 233 determines the azimuth of the projection of light reflected from mirror 235, and its elevation is determined by the position of the mirror as will be explained in connection with FIG. 15.

Referring now to FIG. 17 in some detail, it will be observed that tubular drive shaft 233 is terminated in bevel gear 240 which meshes with bevel gear 241. Both of these rotatable members are supported in a common housing 242 by suitable bearing means 243 and 244 which enable rotation as desired. The use of bevel gears enables a change of direction of the axis of rotation to :a position equal to the ecliptic angle of 23 /2 to provide a correction to the fact that the ecliptic axis of the instrument is arranged 23 /2 off the actual polar axis of the system.

The gear 241 supports a deck 246 on which a mirror support 247 is adjustably mounted by screws 248 and 249. The relative settings of the two screws 248 and 249 enable a positioning of the mirror to its proper elevation at a selected azimuth location, preferably at the intersection of its orbital plane with the ecliptic plane. With the elevation of the planet properly adjusted for this one condition, assuming selection of the proper cam and other design dimensions, it will assume correct elevational positions in every azimuth location. Variation in elevation in accordance with the change in the orbital position of the planet is accomplished through pus-h rod 234 which bears against and acts upon push rod 251 which is slidably supported in an axial location within gear 241. The mirror 235 is pivotally supported on deck 247 by a pin 252, parallel to the plane of the mirror and extending through a flange 247a on the deck and a flange 235a on the back of the mirror. Tension spring 254 connected between the mirror flange 235a and deck 246 urges the mirror toward the deck about pin 252. Push pin 251 opposes the spring and bears against flange 235a between the point of connection of spring 254 and pin 252. The system is so designed that the eflect of push pin 251, as determined ultimately by cam 220, is to produce the required changes in elevation to simulate characteristic departures from the ecliptic plane of the planet simulated. As the structure rotates, deck 246 effectively remains in the reference plane While the mirror in rotating 180 goes from the position shown in solid lines to the position in dashed lines in FIG. 17 being actuated in the course of such rotation into different elevational positions by push rod 251.

It will be clear to those skilled in the art that some place in the orbit of a planet the planet must pass below the horizon and the analog mirror of the present invention is adaptable to employ a modified simple cylindrical shutter member of the general type employed with the analog structure of Patent 3,074,183. Gravity will cause the cylindrical structure to assume position with its axis vertical or its top edge horizontal. Thus by positioning such a shutter so that the top edge simulates the horizon, when the reflected beam falls below the top edge it will be intercepted and not projected.

The color of a planet may be simulated by suitable filter means either at the projector or at some place in the beam path as schematically illustrated in FIG. 18. Similarly, other special effects can be interjected as required.

By way of example in FIG. 7 a Venus phasing device consisting of a transparent disc with radial lines effectively at varying circumferential spacings around the disc varies the amount of light passes in different phases of that planet. More specifically the projector 237b is provided with a disc filter 270 as described, driven by a motor 271 which is synchronized to be in the proper phase for various orbital positions of the planet Venus. As the filter rotates the radial lines allow more or less light to pass according to their circumferential density at each particular position.

In view of the number of axes to be crossed and in view of the fact that three sets of slip rings must be employed, a special switching circuit for minimizing the number of slip rings between the base and the projectors has been devised for use with the present invention. This circuit is schematically represented in FIG. 19 which is representative of a time sharing multiplexing system employing transistor switching in the control of brightness of the various lamps involved.

Referring to FIG. 19 the various lamps employed for the diflerent planet simulating systems are shown by y Of example. It will be observed that additional lamps may be required running into many times the eight lamps illustrated here, particularly when auxiliary projectors are taken into consideration. If it were not for the present system, each lamp would require a minimum of six slip rings and there would be considerable problem relative to the adjustment. In accordance with the arrangement shown in FIG. 19, the lamps are designated 280a through 28011. Each of the lamps is connected to the B+ buss. The lamps is this particular version of the switching circuit, are connected to the collector of transistors 281a through 281k. Groups of four emitters are connected in common through slip rings 282 and 283 to a common connection to the collectors of corresponding transistors 284a through 284k. The emitters of these transistors are connected to a ground or B- buss through variable resistors 285a through 285/2 which enable limitation of current which can flow through the respective transistors to which they are connected. The bases of transistors 284a and 284e are connected to a line 286; the bases of transistors 28412 and 284i are connected to common line 287; the bases of transistors 2840 and 284g are connected to a common line 288; and the bases of transistors 284d and 28411 are connected to a common line 289. Common line 286 is also connected to the bases of transistors 281a and 281e;

common line 287 is also connected to the bases of transistors 281b and 281 common line 288 is also connected to the bases of transistors 281c and 281g; and common line 289 is also connected to the bases of transistors 281d and 2811:. Each of these connections is made through three slip rings since each cross three axes of relative movement on the instrument. In practice a common pair of slip rings may be used for all elements receiving the identical signals such as those on lines 286, 287, 288 and 289. Thus, for example, only one set of slip rings is needed for the signal imposed on the bases of transistors 281a and 281s.

With the circuit of FIG. 19, time-sequence pulses are applied to lines 286, 287, 288, 289 in sequence so that each line is provided with a positive pulse for a quarter of the time and at times different from the times the other lines are pulsed positive. In the course of the positive pulsing the transistors to whose bases these lines are connected are rendered conductive, and when the pulses are not present the transistors are cut off. Thus both transistors related to a given lamp with the same suffix are rendered conductive at the same time so that the lamp will illuminate during that time through the common connection 282 or 283. However, the various lamps will differ in brightness depending upon the setting of their associated variable resistors. Despite the fact that the lamps are on only a quarter of the time, they are on all for equal times, and the relative brilliance remains unaffected and is dependent solely upon the setting of the variable resistors which, therefore, serve as dimmers and may be calibrated accordingly.

Only on lamp in each group .may be effective at a time, but subject to this limitation, as many groups as desired may be provided. It will be obvious that if the lamps were pulsed on only one-sixth of the time, groups of six lamps could be employed, and so forth. Any number of groups of the same size, however, can be employed once a group size is determined.

Specific locations of wiring and slip rings have not been shown on drawings of the instrument because they would tend to'confuse the mechanical structure illustrated. Wiring in all respects is conventional and slip rings employed are preferably standard types commercially available. Location of the slip rings is a matter of choice but usually they are concentrated in one or two places along each of the axes and located where the diameters of the'relatively moveable parts on which they are supported may be kept small. Often they are housed to minimize access of dust and dirt.

Although for various reasons certain types of auxiliary '18 projectors are preferably mounted to rotate with the polar axis, as on planet analog decks 20, many other types of projects require less mobility. Forexample, astronomical triangle projectors, moon projectors of certain types and meridian projectors may be mounted elsewhere on the frame. In accordance with the present invention added flexibility is achieved for such projectors by mounting them on the deck 24 whose position is separately variable about the vertical axis 3 in a manner described above in connection with FIG. 6. It should be observed that along with other controls at the console such as servo control motors, lamp dimmers and the like, a motor control for drive mot-or 58 may be provided. In the same location ammeter 291 may be located to indicate the angular position of deck 24 relative to a predetermined reference position. This is most conveniently done by means of a potentiometer 292 across a power source, for example, so that meter 291 reads voltage. The position of the shaft of potentiometer 292 is caused to vary through gear drive 293 which has gear 294 in mesh with the main drive gear 57 of deck 24 so that as the deck changes position, each successive position indicates a unique resistance or potential for each angular position of deck 24. In this manner the deck 24 may be remotely moved to any desired location for best use of the selected auxiliary projector.

I claim:

1. A planetarium projection instrument for use with a concave projection screen in the form of a generally spherical portion, said instrument including projectors located to project upon the screen, said instrument having three axes of rotation, comprising a fixed base, a frame rotatably supported on the base to rotate about one axis, a support rotatably supported on the frame to rotate about a second axis, a projector mount rotatably supported on the support to rotate about a third axis and at least star projector means capable of projecting the celestial sphere carried by the projector support, whereby any point in the celestial sphere may be projected on any selected point of the screen and by successive relative movements of the instrument parts about one or more of the three axes any desired pattern of movement of the celestial sphere may be simulated.

2. The planetarium of claim 1 in which variable speed drive motors are provided between the members at each of the axes and position sensing means are also provided between the members at each of the axes whereby the effect of the drive motors is immediately observable and correctable.

3. The planetarium of claim 2 in which speed controls for the respective drive motors and position indicating means responsive to the respective sensing means are located in a console which may be located remote from the instrument.

4. The planetarium of claim 2 in which a computer capable of programming a predetermined pattern of movement is provided to regulate the speed controls for the respective drive motors and means responsive to the respective sensing means provide feedback information to the drive motors.

5. The planetarium of claim 4 in which the computer employed is an analog computer capable of producing a predetermined pattern of movement about the respective axes to simulate a predetermined movement of the celestial sphere.

6. The planetarium of claim 5 in which the analog computer employed includes components which may be adjusted to simulate variable parameters in the pattern capable of changing the size of the pattern and in which calibrated means are provided for adjusting those parameters.

7. The planetarium of claim 6 in which resolvers are used as components including means of adjusting variable parameters and means responsive to the sensed positions.

8. The planetarium of claim 7 in which separate resolver outputs are used to drive the respective axis motors and the corresponding sensing means correct the positions of the resolvers to reflect changes in axial position.

9. A planetarium instrument having three axes of rotation, two of which are normal to a third comprising a fixed base, a frame rotatably supported by the base to rotate about a generally vertical axis, a support rotatably supported on the frame to rotate about a second axis, and a projector mount rotatably supported on the support to rotate about a third axis and at least star projector means capable of projecting the celestial sphere carried by the projector support whereby movement about the generally vertical axis will permit any selected meridian to be located at any azimuth point in a planetarium.

10. The planetarium instrument of claim 9 in which the frame rotatably supported on the base to rotate about the generally vertical axis provides a gimbal mount for the horizontally disposed support rotatable relative to the frame.

11. A planet analog for a planetarium instrument simulating the locations of two planets, one of which may be the earth, in a solar-like system, comprising a first planet simulating member, a sun simulating structure rotatable relative to the axis of said first planet simulating member and providing a sun simulating axis which revolves about the axis of the first planet simulating member, a second planet simulating structure rotatably supported on the sun simulating structure and rotatable relative thereto and providing a second planet simulating element on said structure, a line of sight connection element between the first planet simulating member and the second planet simulating element, a first drive means to drive the sun simulating structure rotatable relative to said first planet simulating member and a second drive means to drive the second planet simulating structure rotatable relative to the sun simulating structure.

12. The planet analog of claim 11 in which a cam member is provided between the sun simulating structure and the second planet simulating structure in order to simulate the departure of the plane of orbit of one of the planets from the plane of the orbit of the other planet, said cam being maintained in the same attitude with respect to the fixed reference frame of the planet analog by means causing it to rotate at the same rate as the sun simulating structure rotates but in the opposite direction.

13. The planet analog of claim 11 in which the first planet simulating member is axially fixed in position but independently rotatable on the axis of rotation of the sun simulating rotatable member and the second planet simulating element has a ball-like portion giving universal freedom of movement to the second planet simulating element with respect to the rest of the second planet simulating structure, and the line of sight connection element is connected to the first planet simulating member by means holding a point on the connection element on the axis of the first planet simulating member and rototable about an axis normal to said axis of the first planet simulating member and said connection element includes a slide rod portion extending through the second planet simulating element whereby as the position of the planet changes the slide rod can freely move.

14. The planet analog of claim 13 in which a mirror supporting member is rotatably supported along a parallax axis offset from the axis of the first planet simulating member and the sun simulating structure by an amount proportional to the offset of the same axis of the analog from the polar axis of a planetarium on which it is to be mounted in the same ratio as the planet to planet simulating means in the analog bears to the polar axis to the screen, and a second slide rod parallel to the first slide rod is connected to the mirror supporting member and an element similar to the second planet simulating element and coupled to the first slide rod in the same manner as the second planet simulating element is coupled to the second planet simulating structure.

15. The planet analog of claim 14 in which a portion of the reference frame of the planet analog carries a bearing support for the mirror supporting member which is rotatable as the second slide rod causes it to change position.

16. The planet analog of claim 15 in which the mirror supporting member includes a tubular member which changes mirror azimuth and elevation adjusting rod slidably passing through the tubular member and into engagement with the second slide rod to actuate changes in the elevation of the mirror.

17. A planet analog structure employing a mirror for directing a beam of light from a projector to simulate a planets position, comprising a tubular rotatable mirror support to which the azimuth positions of the mirror are applied and a slidable rod snugly engaged within said tubular member and arranged so that change in axial position adjusts the elevational position of the mirror.

18. The planet analog structure of claim 17 in which the mirror is supported on a rotatable platform at a predetermined angle to the platform and the axis of rotation of the mirror is changed from the axis of the tubular mirror support in which the tubular support terminates in means to translate the axis of rotation of the mirror platform to a position at a predetermined angle to the tubular mirror support.

19. The planet analog of claim 18 in which the angle of the mirror with respect to the platform is adjustable about an axis parallel to the platform, resilient means is provided to urge the mirror toward the platform and a second push rod snugly engaged for axial sliding movement only along the axis of the second bevel gear in position to be actuated by the push rod through the tubular member at one end acts upon the mirror to change F its elevation at the other end.

20. The planet analog structure of claim 19 in which a further adjustment is provided to change the initial setting of the angle of the mirror with respect to the platform.

21. A planetarium instrument comprising a frame, at least celestial sphere projector means rotatably supported relative to the frame and an auxiliary projector table for special effect projectors rotatable relative to the frame independent of celestial sphere projector means, drive means for repositioning the table relative to the frame and sensing means for sensing the position of the table relative to the frame.

22. The planetarium instrument of claim 21 in which control means for the drive motor is located remotely from the instrument as an indicator means associated with the sensing means.

23. A planetarium projection instrument for use with a concave projection screen in the form of a generally spherical portion, said instrument including projectors located to project upon the screen, said instrument having three axes of rotation, comprising a fixed base, a frame rotatably supported on the base to rotate about one axis, a support rotatably supported on the frame to rotate about a second axis, a projector mount rotatably supported on the support to rotate about a third axis and planet projector means and star projector means capable of projecting planets in orbit and the celestial sphere carried by the projector support, whereby any point in the celestial sphere may be projected on any selected point of the screen and by successive relative movements of the instrument parts about one or more of the three axes any desired pattern of movement of the celestial sphere may be simulated.

24. A planetarium instrument having three axes of rotation, two of which are normal to a third comprising a fixed base, a frame rotatably supported by the base to rotate about a generally vertical axis, a support rotatably supported on the frame to rotate about a second axis, and a projector mount rotatably supported on the support to rotate about a third axis and planet projector means and 21 22 star projector means capable of projecting planets in orbit References Cited by the-Examiner and the celestial sphere carried by the projector support UNITED STATES PATENTS whereby movement about the generally vertical axis will 1 61 736 2 1927 Bau r f ld 2 permit any selected meridian to be located at any azimuth 5 3,074,183 1/ 1963 Frank 3545 point in aplane ri m- EUGENE R. CAPOZIO, Primtzry Examiner. 

1. A PLANETARIUM PROJECTION INSTRUMENT FOR USE WITH A CONCAVE PROJECTION SCREEN IN THE FORM OF A GENERALLY SPHERICAL PORTION, SAID INSTRUMENT INCLUDING PROJECTORS LOCATED TO PROJECT UPON THE SCREEN, SAID INSTRUMENT HAVING THREE AXES OF ROTATION, COMPRISING A FIXED BASE, A FRAME ROTATABLY SUPPORTED ON THE BASE TO ROTATE ABOUT ONE AXIS, A SUPPORT ROTATABLY SUPPORTED ON THE FRAME TO ROTATE ABOUT A SECOND AXIS, A PROJECTOR MOUNT ROTATABLY SUPPORTED ON THE SUPPORT TO ROTATE ABOUT A THIRD AXIS AND AT LEAST STAR PROJECTOR MEANS CAPABLE OF PROJECTING THE CELESTIAL SPHERE CARRIED BY THE PROJECTOR SUPPORT, WHEREBY ANY POINT IN THE CELESTIAL SPHERE MAY BE PROJECTED ON ANY SELECTED POINT OF THE SCREEN AND BY SUCCESSIVE RELATIVE MOVEMENTS OF THE INSTRUMENT PARTS ABOUT ONE OR MORE OF THE THREE AXES ANY DESIRED PATTERN OF MOVEMENT OF THE CELESTIAL SPHERE MAY BE SIMULATED. 